In recent years the oil refining industry has shifted to processing a larger quantity of resid. Since the early 1980's many refiners have been processing at least a portion of residual oil as a feedstock in their units and several now crack a full residual oil in their units. Processing resid can drastically reduce yields of valuable products when compared to cracking a light feed.
Several factors are important to resid catalyst design. It is highly favorable if the catalyst can help increase gasoline yields, upgrade bottoms, minimize coke and gas formation, maximize catalyst stability, and minimize deleterious contaminant selectivity due to metal contaminants in resid feedstocks such as nickel and vanadium. It is well known that metal contaminants in oil feedstocks significantly adversely affect the performance of zeolitic cracking catalysts to various degrees depending inter alia on the matrix (non zeolite) portion of the cracking catalyst. Various additives ranging from antimony, tin, alumina and sources of phosphorus have been added to feedstock or incorporated in the catalyst or used in solid particles co-circulated with cracking catalyst particles in the cracking cycle to ameliorate the effects of metals.
While many present day catalysts show good yields of desired products, especially gasoline, even when used with feeds severely contaminate with Ni and V, further lowering of coke and dry gas yields, and in particular hydrogen yields, would be desirable to improve the catalytic cracking process.
U.S. Pat. No. 4,430,199 commonly assigned, Brown et al, teaches addition of a phosphorus compound to a zeolitic cracking catalyst (or component of such catalyst), preferably prior to contamination, or to feedstock to reduce gas and coke make due to contamination by metals. Among the phosphorus compounds was ammonium hydrogen phosphate. In illustrative examples, the catalyst was a rare earth exchanged catalyst commercially supplied by assignee under the trademark HEZ-55. Such catalyst is prepared from precursor microspheres composed of the spinel form of calcined clay mixed with a small amount, e.g., 5% by weight or less of the mixture of microspheres, of the metakaolin form of calcined clay. The mixture is reacted with a sodium hydroxide solution resulting in the crystallization of about 20-25% zeolite Y in a spinel derived matrix. Because the finished catalyst has essentially the same size and shape as the precursor microspheres, the catalyst is referred to as an "in situ" catalyst. See, for example, U.S. Pat. No. 3,506,594, Haden et al, commonly assigned. We found that HEZ-55 catalyst does not exhibit the unique feature of catalysts within the scope of this invention.
U.S. Pat. No. 4,454,241, Pine et al, teaches treating a partially cation exchanged calcined zeolite containing clay derived catalyst preferably of the type allegedly described in U.S. Pat. No. 3,663,165, assigned to the assignee of the subject patent application, with a dihydrogen phosphate anion or a monohydrogen phosphate anion. This phosphorus treatment is applied to a partially cation exchange intermediate of a catalyst and not to fully exchanged catalyst which must subsequently be calcined. This particular phosphorus treatment is intended to increase cracking activity when operating with conventional feed and is not intended to passivate metals when cracking contaminated feed.